Novel Devices ♦ news digest


The net forces between the tiny gold droplet, the solid substrate, and the gas cause the nanowire to grow in a particular direction, she points out. Depending on the size of the gold catalyst, she can create wires that exhibit periodic serrations.


Imec develops strained germanium based FinFETs


The firm’s replacement process on 300mm silicon wafers envisages a possible evolution of the FinFET/trigate architecture for 7 and 5nm CMOS technologies


Depending on the size of the gold catalyst used to make them, Latika Menon’s nanowires will exhibit periodic grooves that resemble common motifs in art. (Images courtesy of Latika Meno)


“It first tries to grow outward, but that gives the gold a larger surface area,” she says. “So now the wire gets pulled in the inward direction, and then the gold gets a smaller surface area, so it grows outward again.” This inward and outward growth repeated itself again and again to create a periodic structure nearly 6 million times smaller than the endless column and is significantly more promising for its use in advanced devices.


“That there is very little implementation of nanowire technology in electronics or optical devices is due to the fact that it’s very hard to control their shape and dimensions,” says Menon. But now that she has a very simple way of controlling growth, the next step is to control the size of the catalytic droplet with which she starts.


Another advantage of Menon’s approach is using what Panaitescu called “macroscopic techniques” to create nanoscale materials, thus making it scalable and inexpensive. “We just control a few parameters and then leave it, let it do it’s natural thing,” explains Menon.


This work has been detailed in the paper, “Vapor- liquid-solid growth of serrated GaN nanowires: shape selection driven by kinetic frustration,” by Zheng Ma et al in Journal of Materials Chemistry C, v. 1 (2013): 2013, 7294-7302. DOI:10.1039/C3TC31776E


At the IEDM 2013 conference, imec reported the first functional strained germanium quantum-well channel pMOS FinFETs, fabricated with a silicon Fin replacement process on 300mm silicon wafers.


The device shows a possible evolution of the FinFET/trigate architecture for 7nm and 5nm CMOS technologies.


Since the 90nm technology, embedded SiGe source/ drain has been a popular stressor method to produce strained Si that enhances pMOS devices. With diminishing device dimensions, the volume to implement stressors in the source and drain has also been severely scaled.


Especially, with thin-body devices like FinFETs, the difficulty is even more pronounced. A possible relief would be to implement highly-strained material directly into the channel itself.


Imec’s solution, growing compressively strained germanium channels on a relaxed SiGe buffer, has already proven to boost the channel mobility, and is also known for its excellent scalability potential.


The use of a Fin replacement process to fabricate the strained germanium channel device makes it especially attractive for co-integration with other devices on a common silicon substrate.


January / February 2014 www.compoundsemiconductor.net 167


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